For example, in the processes of manufacturing a NAND flush memory or a MRAM (magneto-resistive random-access memory), processes of forming insulating films such as aluminum oxide films, magnesium oxide films, and the like are carried out. Sputtering apparatus is used in order to form insulating films with good productivity. In this kind of sputtering apparatus, there is assembled a cathode assembly inside a vacuum chamber that is capable of being evacuated, the cathode assembly having: a target appropriately selected depending on the composition of the thin film to be formed; a backing plate for cooling the target at the time of film forming by sputtering; and an annular shield plate which is disposed to lie opposite to the lower side of that projected portion of the backing plate which is projected outward beyond an outer peripheral end of the target.
This kind of cathode assembly is known, e.g., in Patent Document 1. According to this arrangement, the backing plate is formed of metal such as copper with good thermal conduction, and has a projected portion projected outward beyond an outer peripheral end. This projected portion is fixed to a predetermined position of the sputtering apparatus. In addition, after having assembled the backing plate to the sputtering apparatus, an annular shield plate is generally disposed in a manner to lie opposite to the projected portion in order to stabilize the electric discharging, and the like purpose.
By the way, in an example like the conventional one, in a state in which the cathode assembly is assembled to the sputtering apparatus, there is a clearance between the target and the shield plate. When plasma is caused to be generated inside the vacuum chamber during film forming, the electrons in the plasma will sometimes be electrically charged to the projected portion through the clearance. When the electrons get electrically charged to the projected portion, since the target is an insulating material, there will be generated abnormal discharging due to electric potential difference between the side surface of the target and the projected portion.
It is proposed, e.g., in Patent Document 2, that the outer peripheral portion of the target be covered with a shield plate so that the electrons in the plasma do not get charged in the projected portion. However, since the shield plate is disposed on the side of the plasma (on the side of the substrate) of the target, a so-called re-deposition film will be formed as a result of re-deposition of the sputtered particles by their turning around into the clearance between the outer peripheral portion of the target and the shield plate. There is a problem in that, since this re-deposition film is weak in adhesive force, it will easily be peeled off from the target and therefore that the particles will be generated.